1. Field of the Invention
The present invention relates to a method for producing food products of wheat capable of maintaining freshness for a long period of time.
2. Description of the Related Art
The quality of food products of wheat such as bread deteriorates over time after the production. For example, in the case of bread, the retrogradation after baking and the reduction of a moisture content by evaporation are responsible for the deterioration of the quality of bread over time.
In the prior art, for the purpose of preventing the quality deterioration over time, a larger amount of water within a defined acceptable range or an emulsifier such as monoglyceride (MG) is added to bread dough; the retrogradation of starch contained in wheat flour is controlled through partial breakdown of starch by .alpha.-amylase or the like; and the like.
Effects of addition of water to dough vary depending on the difference between the lots of wheat flour used as a raw material. When using wheat flour of the kind having a large water-absorbing ability, the dough becomes so sticky that ease of handling, production yield and the like may be reduced.
The added emulsifier does not have so much effect on the prevention of the retrogradation. The addition of a large amount of the emulsifier results in an emulsion odor, which impairs preferable aroma and flavor inherent in bread that are obtained by fermentation and baking. The addition of the emulsifier is likely to cause bread to become like a gum, which leads to bad mastication.
It has been confirmed that the addition of an enzyme for breaking down starch, such as .alpha.-amylase, provides increased volume which makes soft crumb, and prevents the retrogradation through partial breakdown of amylose. In this case, however, there are still problems that the dough is slack and that the retrogradation of crumb texture is not satisfactorily prevented. An addition of various hydrolyzing enzymes for improving the quality of bread, such as the starch hydrolyzing enzyme, break down ingredients of wheat flour such as starch. However, excessive breakdown of the ingredients of wheat flour is damaging thereto. Thus, the use of the hydrolyzing enzymes requires a large amount of know-how and strict control of the production process, and/or other optional additives for preventing excessive breakdown of the ingredients of wheat flour.
Examples of other hydrolyzing enzymes include lactase (.beta.-galactosidase) (for example, see Japanese Laid-Open Publication No. 4-207143). However, the use of lactase is not usual (see D. Every, Food Technology in New Zealand, May 1990, p. 19). Lactase splits lactose into glucose and galactose. Glucose is fermentable, and thus may increase product volume. On the other hand, galactose is non-fermentable, but it is believed that it is available for Maillard reactions, and thus improves flavor and color.
Wheat flour naturally contains glycolipids in small amounts, some of which are useful for improving the quality of food products of wheat such as bread. Examples of glycolipids of which the usefulness has been known include monogalactosyldiglyceride (MGDG) and digalactosyldiglyceride (DGDG). These glycolipids are called glyceroglycolipid.
The above-described glycolipids are coupled, for example, in bread to both starch and gluten which form the skeleton of the bread, forming barriers and improving gas and moisture retention properties. The utilization of the above characteristic feature of the glycolipids might enable bread and the like to maintain its freshness for a long period of time. However, the amounts of such glycolipids in wheat flour are very small, and vary among different types or lots of wheat flour. Accordingly, it is difficult to improve the quality of food products of wheat such as bread by utilizing such a characteristic feature of glycolipids naturally contained in wheat flour.